Because forces do not scale linearly with length, our physical intuition can falter at the nanoscale. The textbook example is gravity. Weight is a central design consideration for everything from transportation to personal electronics. At the nanoscale, gravity and inertia are practically nonexistent. In contrast, adhesion can be difficult to achieve between macroscopic objects, but it frequently dominates all other forces at the nanoscale. It is not unusual for self-assembling nanosystems to be held together by nothing more than the surface tension of water.